1. Field of the Invention
The present invention concerns the presentation of medical images at a display, and in particular concerns a method and an apparatus for displaying radiographic and digital fluoroscopy radiographic images automatically with a correct orientation.
2. Description of the Prior Art
Historically in the field of x-ray diagnostics, two techniques have developed. In conventional radiography, a single exposure of a bone structure or the thorax, or some other radiation-attenuating anatomical structure is obtained. The other basic technique is fluoroscopy, wherein a series of images is acquired in real time. Dynamic processes such as gastrointestinal movements can be observed and diagnosed with fluoroscopy.
In an x-ray examination, it is known to employ orientation labels in order to identify the position of the patient in the x-ray exposure that is obtained, because many times the position of the patient during the actual radiation exposure cannot be discerned by viewing the subsequently developed image. Such labels can include side labels (R, L), labels that indicate the direction of the radiation through the patient (AP, PA) or identifiers indicating a rotation or an axis mirroring (flip) of the image.
When a diagnostician (radiologist) is using the exposure for diagnostic purposes, It is important that every change in the orientation of the image that has occurred up to the time that the radiologist used the image must be known to the radiologist, in order to enable an accurate diagnosis. Radiography exposures, however, are generally acquired by radiation technologists (RTs), and are only subsequently diagnosed by a radiologist.
By contrast, in digital fluoroscopy radiography (DFR), the radiologist conducts the examination and makes a diagnosis during or contemporaneously with the examination. During a DFR examination, it is desired to have an optimally good view of the patient by changing the image orientation on the monitor. Therefore, it is desired that only an image re-orientation that occurs in post-processing be displayed. This need for different types of orientation information depending on whether a radiographic examination or a DFR examination has been undertaken has not been of significant consequence in the past, because respectively separate systems were used to generate radiographic images and to generate DFR images. Recently, however, dual mode imaging systems have been developed that allow the same system to be operated in a radiographic imaging mode and in a DFR imaging mode. When these images are supplied to a pre-processing or post-processing computer, they both appear to be arriving from the same source (i.e., the image data acquisition system), and therefore it is a problem to accurately identify the different orientations and reorientations that have occurred in the case of radiographic images compared to the case of DFR images.
In analog radiography, for example, lead letters have been used for position detection, which are placed on the x-ray film and thus are visible in the image. Instead of a film, however, a digital detector is used in digital radiography, but the identification principle is similar. Generally, identification during the actual examination is not necessary in DFR, for the reasons discussed above. Only stored images that are viewed after the actual examination, and have been modified in terms of their orientation, must be identified in terms of orientation. The “output orientation” for the image is the orientation that existed at the time of the image acquisition.